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The pulse picker spindle comes pre-aligned out of the box. Should you wish to re-align the spindle to the beam path (essentially, computing an adjustment to the current Mo calibration), you will need to follow these steps:

1. If the picker is not already aligned in X and Y, perform that alignment first.
2. If the expert panel is not already open, open it using the CNTRL button on the simple GUI (Figure 2).
3. Home the spindle using the pulse picker interface (Figure 1). The spindle is now in the positive closed position.

4. Ensure that you have a way of shining light through the picker, and a way of detecting it.

5. Now, start to nudge the picker spindle in the negative direction by entering into the Move Relative box, followed by <Enter>:

   Code Block
   -5

   In this command, -5 is the number of steps to move from the current position. You can enter any number of steps for this command (1600 steps = 1 rotation, 0.225deg/step).
   The objective in this step is to move the spindle to the point where light just starts to shine through. You can move in finer steps, and in the positive direction, to fine-tune this point. Once the spindle is there, record the current position in motor steps, which is on the expert interface as Motor Steps (C1) (click the green number to refresh it; it does not automatically refresh). Let this number be A.

6. Now, continue to nudge the pulse picker spindle in the negative direction by issuing in the Move Relative box:

   Code Block
   -5

   until the spindle interrupts the light. Nudge it in the positive direction by single steps (enter 1 in the box) until you just see light again. Record the current motor position C1, and call this number B.

7. Compute the average of A and B, and call that number C.
8. Compute a new Magic Motor Offset (Mo) by taking the existing motor offset Mo (from the GUI, click to refresh) and subtracting C from it. For example, if the current Mo is -250, and C is 5, then the new Mo = -250 - 5 = -255.
9. Enter the new Mo value into the box directly adjacent to the Mo readback, and press <Enter> to send that new value to the motor.
10. Press the SAVE button in the upper left of the GUI to save all parameters.
11. Repeat steps 3 through 6 to ensure that the spindle is now centered (A and B should be almost the same). If not yet centered, repeat steps 7 through 10, and re-check.

Figure 1: Pulse picker expert GUI, showing locations of controls necessary for alignment.

Figure 2: Pulse picker mode select GUI, showing location of CNTRL button to get to expert GUI in Figure 1.